2024-02-13 19:44:21
Imagine the tranquility of a morning’s work being broken by an immense ball of fire crossing the sky, generating a flash capable of blinding even the sunlight. Instantly a hot wind makes you feel your skin burning under your clothes. Your survival instinct leads you to run, but in vain. You can’t escape the overwhelming shock wave that arrives a few minutes later, knocking down trees and shaking the structures of buildings. This apocalyptic vision could be a possible scenario if our planet is hit by asteroid 2021 EU that approaches Earth at the end of this month. But that won’t happen.
Although an impact is an extremely unlikely possibility, the approach of this asteroid could be an excellent opportunity for a greater understanding of the importance of monitoring work on these near-Earth objects, so that we can be prepared for potentially dangerous cosmic events. When we understand how science detects and tracks these space rocks, calculating the risks of impact on our planet, we will see that there are no reasons to celebrate the end of the world nor reasons to run in panic through the streets announcing the apocalypse due to the approach of the 2021 asteroid I.
The 2021 EU
[ Órbita do asteroide 2021 EU – Imagem: Reprodução ssd.jpl.nasa.gov ]
2021 EU is an asteroid, measuring about 28 meters, discovered in March 2021 by Pan-STARRS at the Haleakala Observatory in Hawaii. Because it is relatively small, even through large telescopes it appears only as a faint point of light. Therefore, it was observed for only 16 nights, during a close approach to Earth, and then disappeared into the vast darkness of space.
At first glance it may seem frustrating to discover a 30-meter space rock one night and lose sight of it two weeks later. However, this is one of the challenges inherent in monitoring near-Earth objects. The vast majority of asteroids in our cosmic neighborhood were discovered this way.
Rocks of this size, despite the potential damage they can cause here on Earth, are practically imperceptible in the vastness of space. We can only see them when they get close enough to be seen in the mirrors of our large telescopes. And it is only possible to distinguish the asteroid among the thousands of luminous points of distant stars because the asteroid moves.
How an asteroid is detected in space
Although everything in the Universe is constantly moving, including distant stars, the closer the object is, the faster it will move in the telescope’s field of view. In this way, stars practically do not move, even when observed for years. On the planets of the Solar System, we can clearly see their position changing every night. Therefore, the process of searching for asteroids close to Earth consists of recording at least 3 images of the same region of the sky, taken every few minutes. Automated systems scan the images for moving objects and if they identify something that is not in the catalog of asteroids or known artificial objects, an alert is triggered.
Whenever an object is detected, the astronomer or the responsible team sends a notification to the Minor Planet Center (or MPC), the body that centralizes information about the smaller bodies in the Solar System. When the object is a NEO, which stands for Near-Earth Object, the MPC issues an alert to astronomers around the world, so that they can make new observations, collecting essential data for determining the asteroid’s orbit and for the assessment of the possibilities of a possible impact with the Earth.
Impact Risk Assessment
The risk of an asteroid impacting Earth is generally calculated automatically by determining the asteroid’s orbital parameters. In short, these software use orbital data to calculate the object’s future position, including considering the gravitational influence of other bodies in the Solar System.
The possibility of impact is given by the position of the asteroid at the time of its closest approach to Earth. Due to measurement uncertainties, this position is not a point, but rather an area, called an uncertainty ellipse, which indicates where the asteroid may be at that particular moment. If this zone of uncertainty is entirely within our planet, the impact is certain. If the uncertainties are greater and the Earth is inside the ellipse, the possibility of impact is calculated depending on the size of the uncertainty ellipse and the Earth’s position within this area. Obviously, if our planet is outside the ellipse of uncertainty, it means there is no risk of impact and we can get on with life…
Something that occurs quite frequently with the asteroids closest to Earth is that, in an initial assessment, with uncertainty still very large, our planet may appear within the ellipse of uncertainty, where mathematically there is a small risk of impact. Sometimes the chances may increase if new measurements shrink the ellipse but keep the Earth inside it. But with the greater refinement of orbital data and a greater reduction in the uncertainty ellipse, in the vast majority of cases, the Earth ends up outside this ellipse and free from any possibility of impact with that asteroid.
One of the systems that automatically calculates impact risks is Sentry, from NASA. And in Sentry’s ranking of the most dangerous asteroids, 2021 EU currently occupies third place, with a 0.0024% chance of hitting Earth on February 27th. It’s such a small chance that it would be the equivalent of rolling a die 6 times and getting a 6 every time.
Uncertainty and imprecision
However, we cannot categorically say that the asteroid will miss Earth, because there is great uncertainty in the calculations. Each measurement carried out by astronomers has a margin of error, and this margin propagates into orbital calculations. In some cases, such as the 2021 EU, this margin could mean the difference between safe passage 6 million kilometers away and a catastrophic impact with Earth.
To facilitate this understanding, we can use the analogy of drawing a circle based on three points on its circumference. The inaccuracies of astronomical measurements could be represented as a “widening” of these points and with this, several similar circles would be possible passing within the margin of error of the 3 points.
This inaccuracy is magnified when the asteroid is observed for a short period of time, as is the case with 2021 EU. Its orbit, which has a period of about 3 years, was calculated with just 16 days of observation. This is equivalent to drawing a circle based on three points that represent less than 6° of the total circumference, resulting in lower quality orbital data. If we consider the central orbit within the margin of error, 2021 EU should pass about 6 million kilometers from Earth, which is approximately 15 times further away than the Moon.
This inaccuracy should only be reduced when the asteroid is “recovered”, that is, when it is observed again by search programs after completing an orbit around the Sun. If this happens in the next few days, it will certainly remove the possibility of impact, but as this asteroid approaches our planet from the direction of the Sun, the best conditions for observing it should occur during or after its close passage.
Effects of an unlikely impact
[ Rastro de fumaça deixado pelo meteoro de Chelyabinsk visto sobre os Montes Urais, na Rússia – Créditos: Alex Alishevskikh ]
If you are still worried about 2021 EU, I think it is important to remember that it is not even considered a potentially dangerous asteroid. This is not because of the uncertainties of its orbit, but because it is too small to cause significant damage.
Due to its estimated mass of 28 thousand tons and its speed of 87 thousand km/h, if it hit Earth it would have a destructive potential 5 times greater than the asteroid that hit Chelyabinsk in 2013. But this would only have local effects and would only really be catastrophic if it occurred over a city. And as cities occupy only 2% of the planet’s surface, the chances of this actually happening are even more remote.
We can be calm about 2021 EU, but it is important to highlight that this same asteroid has already made more dangerous approaches than this, in 2021 and 2018, without being noticed. This shows us that we must invest more and more in search programs that find and track these dangerous objects for our planet. Because probably the most dangerous asteroid for Earth has not yet been discovered.
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